Technical Field
This invention is in the field of computer modeling of physical objects and, in particular, the generation of a three-dimensional model using one or more two-dimensional photographs as a starting data set.
Description of the Related Art
Several methods can be employed to generate a three-dimensional computer model of a roof in the form of a wire-frame using one or more overhead photographs.
A first method is to trace the image in the photograph with or without user input. Using this tracing method on a photograph that provides a nearly top-down view of the structure of interest, a computer-aided design (CAD) tool allows lines and polygons to be drawn over the background image. The resulting wireframe model reflects the lines and contours of interest in the locations they are observed in the photograph.
While this method has the advantage that it is fast and compatible with many off-the-shelf CAD and drawing tools that do not require much training, there are a number of disadvantages. One disadvantage is that incorrect line lengths on sloped roof facets will result when the image is not taken from directly overhead, resulting in a “lean” of the roof within the image.
Another disadvantage is that there is a poor ability to correctly determine pitches on sloped roof facets.
Other problems are a poor determination of layered or underhanging roof sections. This first method requires a user to have previous knowledge of the roof facet pitches to obtain a wireframe without errors.
A second method is for a user to select and align roof ‘primitives’ over a photograph.
Like the previous method, an overhead photograph is selected as a backdrop starting point for a CAD tool. However, rather than tracing lines and polygons, the CAD tool allows the user to overlay, resize, and connect common geometric roof forms stored as primitives. Gables and hips are examples of commonly found primitive forms used in roof designs. The photograph provides a visual reference for the selection and placement by the user of these higher-level objects.
While this method has the advantage that a skilled operator can produce geometrically correct models, it has the disadvantage that it is harder to create from an image and it becomes more time consuming with increasing roof complexity.
In addition, complex user interface software is required, which requires greater training.
This second method also requires subjective technician judgments by the user to compensate for lean artifacts due to lean and shadows in images.
The user must also have previous knowledge of the roof facet pitches to correctly size the roof.
A third method is for a user to obtain and work with one or more photographs of the same roof taken from different angles in order to trace a 3D wire model of the roof.
This method starts with a set of photographs that are analyzed to derive a virtual 3D volume that is geometrically consistent with all the supplied viewpoints of the target roof. The line segments comprising the wireframe are then drawn in 3D-space and projected back onto the set of photographs to assess the correct placement within the derived 3D volume. The details of this method are described in prior U.S. patent applications owned by the assignee, EagleView Technologies, and bearing U.S. patent application Ser. Nos. 12/148,439; 12/253,092; 12/590,131; 12/467,244; and 12/467,250.
The advantage of this third method is that it does not require previous knowledge of roof facet pitches, rather, pitches are derived from the content of the photograph(s). It also produces geometrically correct models. Unfortunately, the detailed 3D model made this way cannot be easily imported to some widely used home construction CAD software programs.
The disadvantages of this third method are that greater training is required as compared to the first method and it becomes harder and more time consuming with increasing roof complexity without further processing or touch-up of the model to meet import requirements of the 3rd party software. To summarize, the first method provides a fast and simple means of generating a wire frame model of a roof at the expense of decreased accuracy and a dependence on having previous knowledge of the roof facet pitches to complete the model.
The second method sacrifices some speed and ease of use in exchange for a more consistent model and a dependency on having previous knowledge of the roof facet pitches to complete the model.
The third method also sacrifices speed and requires more user skill than the first method, but the resulting model is a very accurate reflection of the correct geometric form of the house in the photograph and does not depend on previous knowledge of the roof facet pitches.